Mungbean Response to Regulated Deficit Irrigation: A Trade‐Off Between Productivity and Adaptability?

ABSTRACT Water scarcity, elevated temperatures, as well as pests and diseases have been demonstrated to have a detrimental effect on the yield potential of mungbean ( Vigna radiata ). The cultivation of improved mungbean genotypes with regulated deficit irrigation (RDI), a water‐saving irrigation strategy, has been identified as a promising approach to enhance yield stability of the crop and ensure food security. Thus, the purpose of this study was to identify adaptation strategies and possible trade‐offs to drought of mungbean genotypes under deficit irrigation and the effect on yield by investigating in particular assimilate re‐allocation. Four genotypes (NM11, AVMU 1604, AVMU 1635, KPS2) were cultivated in a greenhouse under three treatments of RDI with depletion fractions as a percentage of total available soil water (TAW) of 0.45, 0.65, and 0.8, corresponding to a recommended irrigation schedule, moderate and severe water deficit, respectively. Samples were collected at the flowering and maturity stages, and the dry matter, dry matter partitioning, yield, harvest index, pod harvest index, water use efficiency, and carbon‐13 isotope discrimination to estimate transpiration efficiency were determined. The study found that productivity (i.e., grain yield) was not lowered as a trade‐off of adaptability to water deficit irrigation. The genotypes either did not respond to deficit irrigation (KPS2 and AVMU 1635) in terms of grain yield or exhibited increased remobilisation of assimilates, either from pod walls to seeds (NM11) or from vegetative plant parts to pods/seeds (AVMU 1604), thereby increasing yields by 38% and 52%, respectively, under water deficit. However, the genotype KPS2 demonstrated stable yields and the greatest harvest index/pod harvest index (36%/69%) across all RDI treatments, suggesting superior adaptability to fluctuating water availability and efficient resource allocation, providing a suitable choice for a range of environmental conditions.